1. Field of the Invention
The present invention relates to a heat dissipating fan and, more particularly, to a heat dissipating fan including a motor having an inner rotor.
2. Description of the Related Art
Referring to FIG. 1, a conventional heat dissipating fan 70 including an outer-rotor-type motor is shown. Specifically, the heat dissipating fan 70 includes a frame 71 with a shaft tube 711 disposed inside the frame 71 and receiving a bearing 712, a stator 72 mounted around the shaft tube 711, a circuit board 73 mounted around the shaft tube 711 and electrically connecting with the stator 72, and a rotor 74 having a shaft 741 and an impeller 742. One end of the shaft 741 rotatably extends through the bearing 712, and the impeller 742 is mounted to the other end of the shaft 741. The impeller 742 includes a permanent magnet 743 facing the stator 72. The circuit board 73 controls the stator 72 to generate an alternating magnetic field for reacting with the permanent magnet 743, so that the impeller 742 is driven to rotate for heat dissipation purposes.
Said conventional heat dissipating fan 70 is driven by an outer-rotor-type motor. However, in comparison with inner-rotor-type motors, outer-rotor-type motors are generally less stable in rotation and can only provide a lower rotation rate at full speed. However, owing to the current trend of research and development in electronic products, which includes high operation speed, function integrity, and miniaturization, heat dissipation with high efficiency has become an urgent demand. Unfortunately, the conventional heat dissipating fans with outer-rotor-type motors can not fulfill the heat dissipation need of these electronic products.
Taiwan Patent Publication No. 200744290 entitled “FAN AND ITS INNER-ROTOR-TYPE MOTOR” is an example that meets the demand for efficient heat dissipation. As illustrated in FIG. 2, a conventional inner-rotor-type heat dissipating fan 80 includes a housing 81 consisting of a first shell 811 and a second shell 812, a stator 82 having a magnetically conductive member 821, a rotor 83 having a shaft 831 and a magnetic element 832, a driving device 84 electrically connected to the magnetically conductive member 821, and an impeller 85. The shaft 831 is mounted into the housing 81, and the magnetic element 832 inside the housing 81 is mounted around the shaft 831 and faces the magnetically conductive member 821. The impeller 85 is outside the housing 81 and coupled to the shaft 831. The driving device 84 controls the current direction of the magnetically conductive member 821 to cooperate with the magnetic element 832 for generating an alternating magnetic field to drive the rotor 83 and the impeller 85 to rotate.
However, when it is desired to dissipate heat in various electronic products with the heat dissipating fan 80, airflow generated by rotation of the impeller 85 can not be effectively guided to a heat-generating portion in an electronic product since a fan frame is absent from the heat dissipating fan 80. Thus, heat dissipating efficiency of the heat dissipating fan 80 is low.
To overcome the problems of the heat dissipating fan 80 without a fan frame, FIG. 3 shows a conventional heat dissipating fan 90 driven by an inner-rotor-type motor. The heat dissipating fan 90 includes a frame 91 made of plastic material by injection molding, an inner-rotor-type motor 92, an impeller 93 and a circuit board 94. The frame 91 has a fan housing 911 and a motor housing 912 inside the fan housing 911. The inner-rotor-type motor 92 is mounted inside the motor housing 912 and has a shaft 921 with one end thereof extending out of the motor housing 912, a magnetic element 922 mounted around the shaft 921 and a stator 923 surrounding the magnetic element 922 and electrically connected to the circuit board 94. The impeller 93 is outside the motor housing 912 and coupled to the end of the shaft 921 extending out of the motor housing 912. Thus, the inner-rotor-type motor 92 drives the impeller 93 to rotate to dissipate heat.
The frame 91 of the heat dissipating fan 90 is formed by injection molding to guide airflow generated by rotation of the impeller 93. However, since the motor housing 912 of the frame 91 is made of plastic material, the motor housing 912 does not provide sealing effect and allows magnetic flux leakage when the circuit board 94 controls the stator 923 to generate an alternating magnetic field for reacting with the magnetic element 922. Said magnetic flux leakage leads to electromagnetic interference to affect rotating performance of the impeller 93. Hence, heat dissipating efficiency of the heat dissipating fan 90 is decreased.